The present inventors have previously filed an application for a constant pressure regulator that can solve the problems of dust generation due to the contact of parts in a constant pressure regulator and the deterioration of the pressure control performance with a small flow rate, the contents of the application being disclosed in Japanese Unexamined Patent Publication No. 2001-141083.
As shown in FIG. 6, the aforementioned constant pressure regulator includes a body 42 having a first valve chamber 40 and an inlet flow passage 41, a cover member 45 having a second valve chamber 43 and an outlet flow passage 44, a first diaphragm 46 fixed on the upper peripheral edge of the first valve chamber 40, a second diaphragm 47 clamped between the body 42 and the cover member 45, an axially movable sleeve 49 joined to the central portion of the first diaphragm 46 and coupled to an annular coupling portion 50 of the second diaphragm 47, and a plug 52 fixed to the bottom of the first valve chamber 40 and defining a fluid control region 51 between the lower end of the sleeve 49 and the plug 52. The constant pressure regulator has an air chamber 53 surrounded by the inner peripheral surface of the body 42 and the first and second diaphragms 46, 47, and an air supply port 54 communicating with the air chamber 53. The pressure receiving area of the second diaphragm 47 is larger than that of the first diaphragm 46.
In the constant pressure regulator described above, however, the annular protrusion 55 of the second diaphragm 47 can creep and thus the sealing performance of the second valve chamber 43 may be deteriorated with time if the second diaphragm 47 is formed of a material liable to creep such as polytetrafluoroethylene (hereinafter referred to as PTFE) which is suitably used in a line for a corrosive fluid. Also, the use of an elastic material such as rubber often reduces the sealing performance due to the degeneration of the rubber caused by the fluid heat. Further, the structure in which the plug 52 is screwed with the body 42 often reduces the sealing performance of the coupling portion due to the distortion or deformation when a pressure or temperature variation occurs in the first valve chamber 40 for a long time.